Thickening method of an electroforming shim

ABSTRACT

A thickening method of an electroforming shim is provided to increase the thickness of a metal shim. In this embodiment, an active solder with a rare earth element is used to increase the moisture on the substrate surface for the solder during the combining process. Afterwards the oxides of the rare earth element are expelled by mechanical stirring to produce a clean contact surface. The melted fillers moisturize on the substrate surface to achieve the combination.

BACKGROUND

1. Field of Invention

The invention relates to a thickening method of an electroforming shim and, in particular, to a thickening method of an electroforming shim to increase the connection between the metal shim and the metal die using an active solder with ultrasonic waves.

2. Related Art

The optical molding machine is usually combined with the photolithography and electroforming potting technologies. The conventional electroforming machine has a very good affinity. A large electroforming machine with high precision can be accurately produced for repeatedly usable dies. This type of manufacturing process is very simple and involves very few steps.

Electroforming is a chemical deposition technique whose deposition speed follows the Faraday's law. It is known that the deposition speed is affected by such parameters as the current density and composition. However, the optical molding machine has a very high demand on the precision and flatness. Therefore, the current density for electroforming cannot be too high. As a result, the metal deposition speed is slower.

Traditionally, the manufacturing process of the electroforming mold is done by forming an electroplating layer on the surface of a pre-formed mold prototype, followed by mechanically machining the electroforming layer. The molding plate is combined using screws, solder, or fitting, thereby completing the combination of the molding plate with the electroforming mold. However, when combining the molding plate onto the electroforming layer of the electroforming mold, a thicker electroplating layer is usually needed to provide sufficient strength and thickness for providing an appropriate plane to combine with the molding plate during the mechanical machining. To obtain a thicker electroforming layer, a longer manufacturing time is required. For a mold with an uneven surface, the corner effect will result in an uneven electroforming layer too. If one wants to shorten the manufacturing time and only electroforms a thinner electroforming layer, the strength will be insufficient and difficult for further machining. This is inconvenient in product development.

To shorten the mold electroforming time, a common method is vacuum adsorbing, e.g. CD stamper. Here the electroforming shim thickness is between hundreds of micrometers and several centimeters. However, the electroforming shim is adsorbed on the mother mold by vacuum, such that the lifetime of the mold is very limited. Using this method still requires precision back throwing for subsequent machining.

Besides, a physical deposition technique, such as the metal spray technique, is used to thicken the electroforming shim, where the goal of rapid molding is also achieved. To prevent the deformation of the electroforming shim, the required thickness has to be more than several centimeters. Moreover, since the spray layer is a porous layered structure, its strength is insufficient. The deformation produced during the thickening process is not suitable for optical molding machines that have higher demands in deformation and strength.

Therefore, the problem of bonding between the electroforming metal layer and the thickened metal layer needs to be studied. It is preferred to provide a method for rapidly thickening the electroforming metal layer without sacrificing its strength.

SUMMARY

In view of the foregoing, an object of the invention is to provide a thickening method of an electroforming shim to solve problems in the prior art.

To achieve the above object, the disclosed method includes the steps of: acquiring the metal shim and a metal mold; coating two metal layers on the metal shim and the metal mold, respectively; preheating the metal layer coated metal shim and metal mold; coating two layers of active solder on the joining surfaces of the preheated metal shim and metal mold, respectively; using a mechanical stirring method to pre-moisturize the metal shim and the metal mold; and connecting the joining surfaces of the metal shim and the metal mold.

The active solder contains rare earth elements. The material of the metal shim can be copper (Cu), nickel (Ni), iron (Fe), cobalt (Co), and their alloys. The material of the metal mold can be Cu, Ni, carbon steel, die steel, zinc (Zn), aluminum (Al), their alloys, and stainless steel. The metal layer for increasing the soldering can be made of tin (Sn), indium (In), silver (Ag), and Cu.

The coating of the metal layer can be achieved by electroplating, electroless plating, evaporation, chemical vapor deposition (CVD), physical vapor deposition (PVD), and metal spray.

The mechanical stirring method is to impose an ultrasonic wave. Therefore, one may utilize an ultrasonic soldering machine to perform the step of pre-moisturizing.

In one embodiment of the invention, the metal shim and the metal mold are disposed on a hot press machine for preheating. The preheating temperature is determined by the materials of the metal shim and the metal mold. It is between 220□ and 400□, and preferably set at around 250□.

Using the disclosed method can rapidly thicken the electroforming optical mold. Before the electroforming metal shim and the thickening metal mold combine, one does not need to perform mirror polishing. Moreover, the electroforming metal shim and the metal mold combine into one body, instead of temporary adsorbing. Therefore, it is useful in elongating the mold lifetime.

According to the disclosed method, there is no deformation problem because the process can be done at low temperatures. Moreover, the time for making the electroforming mold can be greatly reduced. The combination of the electroforming metal shim and the thickening metal mold can be implemented using cheap electroforming equipment, hot press equipment, and the ultrasonic soldering machine. Thus, the production cost can be reduced and the process can be simplified. It is tested that the combined metal shim and metal mold still have a high strength.

Since the disclosed method does not need to use any flux, the manufacturing process is environmentally friendly. Moreover, the combination needs not be performed under a specially prepared state, such as a protective atmosphere or vacuum. Therefore, it ca achieve the requirement of a single process.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given herein below illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1 is a flowchart of the disclosed thickening method of an electroforming shim in a specific embodiment;

FIG. 2 is a flowchart of the disclosed thickening method of an electroforming shim in another embodiment;

FIG. 3 is a schematic view of the test plate formed by a thickening method of an electroforming shim according to the invention for a shearing strength test; and

FIG. 4 shows the relation between the ultrasonic oscillation time and the shearing strength for the test plate in FIG. 3.

DETAILED DESCRIPTION

We first explain the main idea of the invention. The primary connection mechanism is implemented by a property of the affinity between the rare earth elements and oxygen to increase the moisture on the substrate surface for the solder. Afterwards, a clean contact surface is obtained by eliminating the oxides of the rare earth element, such that melted fillers moisturize the substrate for the combination. In other words, a rare earth element is added into the solder to obtain an active solder, which along with ultrasonic vibrations and energy transmission increases the moisture of the solder on the substrate during the combination process. The rare earth element has a reaction with the oxides on the substrate to destroy the oxide structure thereon. A mechanical stirring method is employed to expel the oxides of the rare earth element, producing a clean contact surface. The melted fillers moisturize the substrate to facilitate the combination.

FIG. 1 shows a thickening method for an electroforming shim according to an embodiment of the invention. First, a metal shim and a metal die are acquired (step 110). Metal layers are respectively coated thereon to increase the soft-soldering property of the metal shim and the metal die (step 120). The metal shim and the metal die are preheated (step 130). Layers of active solder are respectively coated on joining surfaces of the preheated metal shim and the metal die, wherein the active solder contains a rare earth element (step 140). A mechanical stirring method, such as ultrasonic waves, is employed to pre-moisturize the active solder coated metal shim and metal die, discharging the oxides of the rare earth element on the joining surfaces of the metal shim and the metal mold (step 150). Finally, the two joining surfaces are pressed together (step 160).

Before step 110, the metal shim is obtained in an electroforming method. First, a preformed mold prototype is provided (step 102). The mold prototype is immersed in a conductive solution after having the conductivity, thereby forming a metal shim on the surface of the mold prototype (step 104). The mold prototype is then departed from the electroforming metal shim, leaving the desired metal shim (step 106), as shown in FIG. 2.

In step 120, the coating of the metal layer can be achieved by electroplating, electroless plating, evaporation, chemical vapor deposition (CVD), physical vapor deposition (PVD), and metal spray.

In step 130, the metal shim and the metal die are disposed on a hot press machine for preheating. The preheating temperature is determined by the materials of the metal shim and the metal. Its range is between 220° C. and 400° C., and preferred to be around 250° C.

In step 150, an ultrasonic soldering machine is used for pre-moisturizing. The material of the metal shim can be copper (Cu), nickel (Ni), iron (Fe), cobalt (Co), and their alloys. The material of the metal mold can be Cu, Ni, carbon steel, die steel, zinc (Zn), aluminum (Al), their alloys, and stainless steel. The metal layer for increasing the soldering can be made of tin (Sn), indium (In), silver (Ag), and Cu.

Through an application of the thickening method for an electroforming shim, as shown in FIG. 1, an electroforming nickel plate (i.e. the metal shim) and a die steel, SKD11, (i.e. the metal mold) are integrated, such that the goal of thickening the electroforming nickel plate is achieved. The combined electroforming nickel plate and the die steel then go through various tests and observations.

FIG. 3 shows the size of a test plate (the combination of an electroforming nickel plate and a die steel) in a shearing strength test. FIG. 4 shows the relation between the ultrasonic oscillation time and the shearing strength after the test in FIG. 3. It is observed that the shearing strength depends upon the ultrasonic oscillation time. After 15 seconds of ultrasonic oscillations, the shearing strength reaches 25.03 Mpa or 3625 psi.

In the test of the combination strength, when the connection area is 176.7 mm², the combination force is 396 kg f as obtained from a slow stretching experiment. It is then converted to give combination strength of 21.96 Mpa or 3,228 psi.

In summary, using the disclosed method can rapidly thicken the electroforming optical mold. Before the electroforming metal shim and the thickening metal mold combine, one does not need to perform mirror polishing. Moreover, the combination needs not be performed under a specially prepared state, such as a protective atmosphere or vacuum. The electroforming metal shim and the metal mold are combined into one body. Therefore, the invention achieves the requirements of being environmentally friendly and a single process. It is also tested that using the disclosed combination method can achieve high combination strength. There is no deformation problem because the process can be done at low temperatures. Moreover, the time for making the electroforming mold can be greatly reduced.

In addition, the invention can be used to rapidly make such optical molding machine as the light-guiding plate. During the manufacturing process, the time for the electroforming mold to be electroformed in a tub is greatly shortened. Therefore, it is suitable for mass or medium-mass productions or small-amount tests. Besides, the electroforming shim is not temporarily adsorbed in the thickened mold. It is therefore helpful in elongating the mold lifetime.

Using the invention only requires cheap electroforming equipment, hot press equipment, and the ultrasonic soldering machine. Thus, the production cost can be reduced and the process can be simplified.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 

1. A thickening method of an electroforming shim for increasing the thickness of a metal shim, comprising the steps of: acquiring the metal shim and a metal mold; coating a metal layer on the metal shim and the metal mold, respectively; preheating the metal shim with the metal layer and the metal mold with the metal layer; coating a layer of active solder on two joining surfaces of the metal shim and the metal mold, respectively; pre-moisturizing the metal shim and the metal mold using a mechanical stirring method; and combining the joining surfaces of the metal shim and the metal mold.
 2. The thickening method of claim 1, wherein the active solder contains at least one rare earth element.
 3. The thickening method of claim 1, before the step of acquiring the metal shim and a metal mold, further comprising the steps of: providing a preformed mold prototype; immersing the mold prototype in a conductive solution to electroform the metal mold on its surface; and separating the mold prototype and the electroformed metal shim to acquire the metal shim.
 4. The thickening method of claim 1, wherein the step of coating a metal layer is achieved using a method selected from the group consisting of electroplating, electroless plating, evaporation, chemical vapor deposition, physical vapor deposition, and metal spray.
 5. The thickening method of claim 1, wherein the material of the metal shim is selected from the group consisting of copper, nickel, iron, cobalt, and their alloys.
 6. The thickening method of claim 1, wherein the material of the metal mold is selected from copper, nickel, carbon steel, die steel, zinc, aluminum, their alloys, and stainless steel.
 7. The thickening method of claim 1, wherein the material of the metal layer is selected from the group consisting of tin, indium, silver, and copper.
 8. The thickening method of claim 1, wherein the step of pre-moisturizing the metal shim and the metal mold using a mechanical stirring method is the step of pre-moisturizing the metal shim and the metal mold using ultrasonic waves
 9. The thickening method of claim 1, wherein the step of pre-moisturizing the metal shim and the metal mold using a mechanical stirring method is the step of pre-moisturizing the metal shim and the metal mold using an ultrasonic soldering machine.
 10. The thickening method of claim 1, wherein the step of preheating the metal shim with the metal layer and the metal mold with the metal layer is the step of preheating the metal shim with the metal layer and the metal mold with the metal layer using a hot press machine.
 11. The thickening method of claim 1, wherein a preheating temperature for the metal shim and the metal mold in the step of preheating the metal shim with the metal layer and the metal mold with the metal layer is determined by the materials of the metal shim and the metal mold.
 12. The thickening method of claim 11, wherein the preheating temperature is between 220° C. and 400° C.
 13. The thickening method of claim 12, wherein the preheating temperature is preferably around 250° C. 